Electric switch



Sept. 26, 1961 c. A. BURRUS ELECTRIC SWITCH Filed Dec. 29, 1959 FIG. 3

T0 QC. SOURCE Zla PULSE 0U TP U T wvewroe By C. A. BURRUS A T TORNEVUnited States Patent 3,002,069 ELECTRIC SWITCH Charles A. Burrus, RedBank, NJ., assignor to Bell Telephone Laboratories, Incorporated, NewYork, NY, 'a corporation of New York I Filed Dec. 29, 1959, Ser. No.862,525 1 Claim. (Cl. 200--112) This invention relates to electricswitches and, more I particularly, to electric switches of the mercurycontact type. I 7

An object of this invention is to provide an improved mercury contactfor use in an electric switch. 7

Another object of the invention is to provide an improved mercurycontact switch capable of extremely rapid cyclical operation.

,Still another object of the invention is to provide an improved mercurycontact switch which is particularly adapted to form the centerconductor of an electric coaxial line. s

A further object of the invention is toprovide an improved mercurycontact switch for use in producing a train of pulses each of very shortduration and having extremely fast rise time.

These and other objects of the invention are accomplished by mounting abifurcated member at the bottom of an essentially cylindrical glassenvelope or housing of an electric switch. The glass envelope is closedat each end and its lower portion contains a pool of mercury surroundingthe bifurcated member which is of such dimensions that the upper ends ofits forks project slightly above the surface of the pool of mercury. Due

to the effects of surface tension and capillary action, a thin sectionof mercury is formed between the forks in an elevated position withrespect to the surface of the pool as is more fully describedhereinafter. The elevated section of mercury functions as one of the twocontacts of this switch.

The other contact of the switch is constituted by the tip of a movablearmature'which is suspended from the top of the glass envelope in such amanner that its lower end or tip extends into the elevated section ofmercury but deos not quite reach the surface of the pool. This armatureis adapted to be electromagnetically controlled or operated so that itslower end will swing transversely through the elevated mercury section;The movement of the armature through the mercury section is facilitatedby providing the end of the armature with a knife like edge.

During the operation of this switch, the armature cyclically swings backand forth rapidly between the forks of the bifurcated member and intoand out of the elevated mercury section. When the armature is in thesection of mercury, an electric connection is made. This connection isbroken when the armature swings out of the mercury section. Thus, theoperating time consumed in making and breaking a connection is only thefew millimicroseconds required for the knife-edge of the armature toslice through the thin elevated section of mercury. It is to be notedthat two connections are made FIGS. 3 and 3A are sectional viewsof thelower por- 3,002,069 Patented Sept. 26, 1961 ice tion of the switchshowing a modified construction thereof; and

FIG. 4 is a schematic diagram partly in section illustrating the mannerin which the switch of FIG. 1 is incorporated in a discharge line typeof pulse generator.

While the invention is not limited to a switch of any given size orproportions, it should be noted that this switch is particularly usefulwhen it is connected in series with the center conductor of an electriccoaxial line. For this purpose, the switch may be made with extremelysmall dimensions, and it should therefore be understood that the figuresshown in the drawing are greatly enlarged in order to facilitate aclearer comprehension of'the construction ofthe switch.

The illustrative embodiment of the invention shown in FIG. 1 isrepresented as an electric switch 1 having an essentially cylindricalglass envelope or housing 2 which is closed at each end. In thisembodiment of the invention, the envelope is about one and three-eighthsinches long and has an outside diameter of approximatelythree-sixteenths of an inch. Two terminals 3 and 4 are mounted inopposite ends of the envelope 2 with a portion of each extending insidethe envelope 2 and another portion projecting outwardly therefrom. Theseterminals 3 and 4are electrically conductive and are made of anyappropriate material, such as an alloy of nickel and iron,

, having substantially the same coefficient of expansion as the glassenvelope 2 so that the joints between the terminals 3 and 4 and theenvelope 2 will form a gas-tight seal. Prior to the sealing operation, asuitable gas, such as hydrogen is introduced inside the envelope 2 underhigh pressure for the purpose of improving the operating characteristicsof the switch 1 and for prolonging its useful life. Two electricconductors 5 and 6 are connected respectively to the terminals 3 and 4in any suitable manner. These conductors 5 and 6 constitute part of anelectric circuit that is controlled by the switch-1. The portion of thelower terminal 3 that extends inside the envelope 2 supports a U-shapedenvelope 7 of magnetic material which is not wettable by mercury. Thismember 7 is securely fastened to the terminal 3 in any convenientmanner. The interior bottom portion of the member 7 serves as a baseupon which is fixedly mounted, in any suitable manner, a bifurcatednonmagnetic member 8, having a thickness of between three fthousandthsof an inch and one hundredth of an inch. These members 7 and 8 arealmost completely submerged in a pool of mercury 9 contained in thebottomof the envelope 2 which serves as a reservoir.

As is indicated in the drawing, a small section 10 of mercury is raisedor elevated above the surface of the pool 9 and is supported in thespace between the forks of the member 8 due to the effects of surfacetension and capillaryaction. In order to facilitate wetting of ,theforks of the member 8 by the mercury, the member 8 is. made of coppercoated with platinum. In this embodiment of the invention, the insidespacing between the forks of the member 8 is about two hundredths of aninch and the top of the elevated mercury section it) is about fourhundredths of an inch above the surface of the mercury pool 9. As wasstated above, this minute elevated met- I cury section 10 constitutesone of the two contacts of the switch 1.

5f the elevated mercury section and the surface of the pool ofmercury-9: In-this embodiment'of the invention, the bottom of the tip 12extends about two hundredths of an inchinto the elevated mercury section102' For the purpose of'facilitating' the movement of the armature 11through the mercury section 10,. its lower end is formed in a sharp,tapered point'or tip'12 and is provided with a knife-like edge so thatit can easily and quickly slice through the mercury section Ill-withaminimum of resistance. Since the tip 12' forms the other contact of theswitch 1, it is coated with anv appropriate material, such as platinum,so that it can be easily wetted by. the mercury. The 'armaturefil'l isjoined to the terminal. 4 by a section 13. of spring steelwelded'theretoso.

as. to increase its flexibility andthereby to increase. the

rapidity of its vibration or. movement.

Movement of the reed or armature 11; is. effected by means of a drivingcoil or winding 14. whichisfconnecte'd' to a. source 14a of alternatingelectric. curreutihaving; the:

same frequency as the. resonantfrequency of. the. reed.

.11, which, in this example, isone kilocycle. By thus.

using an alternating currentsupply 114a having the; same frequency asthe resonant frequency of the reed 11,,it is possible for the reed -11to. obtainits maximum. amplitudev ofsswing while it is vibrating therebyinsuring thatitwill Itv shouldv beknotedthat the upright portions of.the. U.-Shaped morn-- swing completely away from. the mercury.

the-drawing for the purpose-of: simplicity,.itaisto be-understood thatthe coil 14 may actually consist of 'a sole-- noid; having a largenumber. oflturnss Thexdriving action of the. coi1;14 is assistedbytwoper.- manent' magnets 15 and 16 which; are. located outside the. glass"envelope 2. in close proximity to the pool 9 of. mercury. The magnets.15 and16. are-.disposedon opposite' sides of the BRVGIOPEfZ'Wlth theirendsafacing the broad sides of the LI-shaped: member 7,..which, ast-wasstated above, is made of magnetic material. The magnets 15 and 16 arefurther arranged; so? that their ends which are adjacent to the envelope2. are: of opposite polarity. Due to the magnetic forceinduc'ed by the:magnets-v15 and 16, the two upright portionssoi the u-shaped member 7function aspole-pieces.

At this point, it is appropriate to state that the function of theU-shaped' member 7, which is'of'ma'gnetic material, is to enhance thefields of the externalmagnets 15. and 161- If desired, the member 7 canbeomitted provided stronger magnets are substituted for. the magnets 15and 16. Such a modification of the interior'constructionbf. the switch 1is illustrated in FIGS. 3- and 3A. In this form of'the switch 1, it isconvenient to havethe bifur-' cated member 8' directly supported on,or'attached' to, the upper end of the lower terminal 3.

From the above description of the structure of theswitch 1, it can beunderstood that the'electric pa'thbetween the leads 5 and 5' is closedthrough the switch 1' thd mercury section 10. It isto benotedthat'theplatinum coating on the'tip 12' is readily wettable' by'themer oury" thereby assuring that good electric contacts are made. Whenthe tip 12 moves away, themercury'scction 10 becomes broken or disruptedbut it.quickly resumes: its elevatedposition. Asthearmature 11 swingsback, its up 12 again enters the mercury section 10 and briefily reestablishes the electric connection. Thi's connection is ofvery shortduration because the.- tip 12 quickly slices through the extremely thinmercury section. 10. Since the-amount of mercury containedinitheelevatedlsection 10 is so'minute and is so thin, it presentsnegligible resistance to the passagemf the tip 12 and, consequently,;

' ductor of a coaxial line since it can thenfunction as a pulsegenerator. for producing pulses; with extremely fast rise time and ofvery shortdurations The manner in which the switch 1 is installed forthis purpose is illus trated in FIG. 4 which shows a discharge-line typeof pulse generator comprising an open-circuited coaxial'line constitutedby an outer cylindrical conductor 17 of non magneticmaterial surroundingan inner-coaxial conductor 18. to conductors S and 6, the terminals 3and 4 are now connected in serieswith the inner coaxial conductor 18.

This can be done in any convenient-manner, such asby welding.The"function-performedby the magnets 15 and 15', shown-in FIG. 1, is'accomplished by'similar magnets" 19 and 20 which" are attached to theouter coaxial" con-- doctor 17. v

In this embodimentof'the invention, the driving coil 14 of FIG. 1 is.replacedby a driving sol'enoidZl formed around the outside ofthe'outerconductorl? andhaving switch terminal 4", is also connectedthrougharesistor'n' to a source 23 ofdirect currentvoltage which appliesa" charge to this open-ended coaxial line.17-18; Djure ing operation,the charged coaxial line 17-18 iscyclica'h 1y discharged attlie rateofZOOtimes in one secondby the switch. This-produces a train ofvery'short pulses each havinganunusually fast rise time and each havinga length equal't'o or less than the time required for the reed tip 12 toslice through the elevated mercury section It}.

The. switchi is particularly adapted for forming part of'acoa'xiallline: as it hasa substantially uniform crosssection along its.length. This. construction minimizes reflections that might otherwise.vbe caused'by an impedance mismatch along the line and is therebyconducive tothe production of. pulses having the desired sharp shape.The pulse shape is further improved. due to the fact that thestructureof the switchv 1. as was explained above is suchthat it produces. nocontactchatter during operation of the switch 1. a

What is claimed is: 7

An. electric switch. comprising an. envelope. member. containing at oneend" a pool of: mercury, aterrninal having a portion extending outsidesaide'nvelope and-another portionprojecting inside said. envelope and.sub.- merged in said pool,. a. U-shapedmember. of magnetic materialpositioned in. said pool and attached to the: terminal portion. therein,said. U-shaped member having. two arms and aninterior bottomportiommeansfor. elevating a section of said-mercury above the surface of said. poolwith the bottom of. saidsection contiguous with the surface of saidpool, said means comprising a bifurcated member of non-magneticmaterialhaving'forked .portions,.. said. bifurcated member being mountedon-theinterior bottom portion of said U-shapedmember andbetween the armsthereof, the forked portionsof saidbifurcatedmemher. being so.proportioned as to project above the tops'of the arms of. said. U-shapedmember. and. also to. protrude above.- the surface-of said pool whiletheir bottom portions remain submerged in-saidpool of mercury, mag neticmeans external to said envelope for oppositely, polarizing the arms ofsaid U-shaped member, an armature of magnetic materialmounted abovesaidpoolformove- Instead of ccnnecting'the switch terminals 3' and 4- mentof its tip transversely between the forks of said bifurcated member, andelectromagnetic means external to said envelope for cyclically changingthe polarity of said armature tip, said armature having a lengthsulficient for the maximum downward extent of travel of its tip to reachonly to an intermediate point between the References Cited in the fileof this patent UNITED STATES PATENTS George June25, 1957

